1. Field of the Disclosure
Generally, the present disclosure relates to integrated circuits, and, more particularly, to enhanced temperature control techniques in semiconductor devices.
2. Description of the Related Art
The fabrication of integrated circuits requires a large number of circuit elements, such as transistors and the like, to be formed on a given chip area according to a specified circuit layout. Generally, a plurality of process technologies are currently practiced, such as CMOS technology for complex circuitry, such as microprocessors, storage chips, ASICs (application specific ICs) and the like, bipolar techniques, a mixture of these techniques and the like, wherein, due to recent advances, complex systems may be formed on a single die, which may also comprise complex analog circuit portions. During the fabrication of complex integrated circuits using any appropriate technology, millions of transistors, such as N-channel transistors and P-channel transistors in MOS technology, bipolar transistors, diode structures and the like, are typically formed on a substrate including a crystalline semiconductor layer. A transistor, irrespective of whether field effect transistors or bipolar transistors are considered, comprises so-called PN junctions that are formed by an interface of highly doped regions, such as drain and source regions, with an inversely or weakly doped region, such as a channel region, disposed between the highly doped regions. The overall conductivity of the transistors, i.e., the drive current capability, is controlled by a gate electrode or a base terminal by applying an appropriate control voltage or control current. Since the critical conductive paths within the transistors are provided in the form of doped semiconductor regions, the overall behavior of the individual transistor elements strongly depends on the temperature of the semiconductor material, wherein, in bipolar transistors, conductivity may increase with increasing temperature, while, in MOS transistors, an inverse relation between drive current and temperature may typically be observed. Although temperature stability of circuit portions may be significantly increased by appropriately designing the basic circuit function and applying sophisticated layout concepts, nevertheless, advanced temperature controlling may be required.
For example, the increased packing density of integrated circuits resulting from the reduced device dimensions has given rise to the incorporation of more and more functions into a single semiconductor die. Furthermore, the reduced feature sizes may also be accompanied by reduced switching speeds of the individual transistors, thereby contributing to increased power consumption in MOS circuits, since the reduced switching speeds allow the operation of the transistors at higher switching frequencies, which in turn increases the power consumption of the entire device. In sophisticated applications using densely packed integrated circuits, the heat generation may reach extremely high values due to the dynamic losses caused by the high operating frequency in combination with a significant static power consumption of highly scaled transistor devices owing to increased leakage currents that may stem from extremely thin gate dielectrics, short channel effects and the like. Therefore, great efforts are being made in order to reduce overall power consumption by restricting the usage of high performance transistors, which usually cause higher heat generation, to performance critical signal paths in the circuit design, while using less critical devices in other circuit areas. Moreover, appropriate mechanisms may be implemented to operate certain circuit portions “on demand” and control local or global operating conditions depending on the thermal situation in the semiconductor die. Since external heat management systems may not enable a reliable estimation of the die internal temperature distribution due to the delayed thermal response of the package of the semiconductor device and the possibly insufficient spatial temperature resolution, respective external concepts may have to be designed to take into consideration these restrictions and provide sufficient operational margins with respect to heat control or to risk overheating and thus possibly destruction of specific critical circuit portions.
Manufacturers of semiconductor products, therefore, increasingly prefer accurate internal temperature measurements that do not substantially depend on external device conditions and dedicated thermal hardware components that may be subject to external tampering, while also avoiding the slow thermal response via the device package. For this purpose, sophisticated heat monitoring regimes may typically be incorporated into the overall design of the integrated circuit, which may enable a device internal heat management irrespective of external conditions. Thus, die internal temperature measurements are typically performed in complex devices, such as CPUs, ASICs and the like, so as to provide device internal data for controlling the overall operation by reducing operating frequency, switching off respective circuit portions and the like.
Consequently, great efforts are being made in view of enhancing temperature management within integrated circuits for given heat dissipation capabilities of the integrated circuit chip and its environment substantially without sacrificing performance of the integrated circuit. On the other hand, the increasing miniaturization of advanced integrated circuits and the corresponding gain in performance and functionality associated therewith may enable the usage of integrated circuits in a wide field of applications which may have previously been excluded. For instance, complex embedded systems, low power applications in mobile devices and the like are rapidly growing fields in which sophisticated integrated circuits are used, and will increasingly be used in the future. Due to the wide variety of possible applications of these devices, very different environmental conditions may be encountered during operation of the devices, such as mobile computers, mobile communication systems with a high degree of complexity and the like. Consequently, many integrated circuits, or at least significant portions thereof, which may have been designed with respect to well-defined environmental conditions and in particular with respect to well-defined temperature ranges, the application of these circuit designs may not be “portable” to more sophisticated environmental conditions without significant redesign, which may therefore result in increased cost due to extensive circuit simulations and resulting reconfiguring of well-established circuit portions. Typically, the semiconductor manufacturers are mostly concerned with high temperature environments which may be caused by the self-heating of the integrated circuit itself, possibly in combination with externally supplied heat, wherein typical in-die thermal sensing circuitry may be provided, as previously indicated, in combination with passive cooling systems within a die and the package of the integrated circuit, which may then be assisted by active cooling systems provided in the periphery of the integrated circuit. However, little attention has been given to the operational behavior of complex circuitry at low temperatures, which may increasingly be encountered as the number of portable devices, such as laptops and embedded system, is growing. Consequently, an increasing number of mobile systems or any other systems may potentially be used in cold environments, which per se would not represent an issue if individual circuit elements would be considered, which, however, in a complex system including a CPU, possibly in combination with analog circuitry, such as phase locked loop units (PLL), delay locked loop units (DLL) or resonant components (RLC) may suffer from performance deterioration. For example, a mobile computer may be stored in a car overnight at a cold temperature and may then be switched on before the system is brought to a temperature range for which the basic circuit portions of the mobile computer are designed. In other cases, using complex systems in cold climates, such as Alaska or Siberia, may cause significant issues with respect to device reliability and performance, since although individual components of the system may have temperature ratings that may cover the encountered environmental conditions, a system as a whole may not necessarily function properly, for instance due to subtle process variations during the fabrication of a certain line of products. Increasing the temperature range for a reliable operation of complex systems, however, may require significant redesign of circuit portions, such as clock trees and the like, which may therefore require moderately long development times due to voluminous circuit simulations, thereby contributing to significant production costs.
The present disclosure is directed to various devices and methods that may avoid, or at least reduce, the effects of one or more of the problems identified above.